1. Field of the Invention
The present invention relates to a gain modulated sense amplifier, particularly for memory devices.
2. Discussion of the Related Art
It is known that in a memory device the sense amplifier is the circuital element that is meant to sense the data in the memory matrix and then capture the data when the correct reading values are reached.
In dynamic sense amplifiers, characterized by latch memory structures, it is very important to determine the moment of data sensing and the sensitivity of the amplifier, i.e., the timing of the control step used for data capture, so as to obtain the best possible result in any operating condition.
The sensing step generally occurs after a first precharging step that very quickly brings the various bit lines, to which the various memory cells are connected, to the operating level and equalizes them. Indeed because they are equalized, these lines must have adequate time to assume a difference, however small, that allows certain and correct data reading.
However, the time intervals that determine a timing for reading a non-volatile memory are not absolute and depend on a certain number of variables, such as: the conductivity characteristics of the memory cells; the levels transmitted to the cells at the given instant; the capacitance of the associated lines; the minimum sensitivity of the sense amplifiers; the impedances of the memory access paths; the presence/absence of supply voltage boosting circuits; the operating temperature.
It is therefore evident that it is not possible to establish beforehand a given data sensing timing, with the purpose of optimizing the read times of a memory device.
Even if timing of the sensing step is considerably expanded, consequently slowing data capture, the case may occur in which the voltage levels transmitted to the cells are still insufficient to determine their conductivity. If the reading operation was executed during this case, the result of the reading operation would be unreliable.
A memory device with cells which are scarcely conductive requires a longer settling time than a similar device with cells which are more conductive. In any case, the sensing step must be followed by a data capture step that must be performed as quickly as possible.
What is needed, therefore, is a device which modulates the data sensing timing which allows the device to adapt the data reading times to the actual conductivity of a memory cell in the various operating conditions.